NSBU help
- Thread starter Jsle131
- Start date
Cool article here - if you wanted to look inside the NSBU switch and see how it works. It's just wipers running against metal, and it's very clear why both trans and NSBU need to be in neutral before installing.
https://gearsmagazine.com/magazine/being-neutral-the-allison-nsbu-switch/
https://gearsmagazine.com/magazine/being-neutral-the-allison-nsbu-switch/
I did what Ron said to do and load tested the grounds in Zone 4, light bulb was nice and bright. I have continuity between pins E&G on the switch while in park.
No power at relay pins 85 and 86.
I hooked my voltmeter up to Pin E on the NSBU and loosened the bolts and moved the switch around with the key turned to start to see if it would change anything, no voltage no matter what way I moved it. Plugged everything back in and the truck cranked over started. Still won't recognize when it's in gear though Im being to think that the new 7 and 4 pin connectors I installed aren't making a good connection.
Trying to help out and follow here. In post #2 you stated you had +12V power on both pink wires of the NSBU, which would be C2-E and C2-C. Now you're saying there's no longer power on C2-E? Please clarify.
Still have power at C2-E. I read the article that you posted and tried clocking the switch to see if I would get any voltage at the dark green wire. Sorry about the confusion in post #24 that should say Pin G not E. After nothing changed while moving switch around I plugged everything back in and magically the truck cranks and runs.
I set up a bench test on the original black switch and the switch I got from Rockauto. With the black switch I hooked power to pin E, Ground to pin D, wire from pin G running to light bulb and grounded the other side of the light bulb to a battery. With the nsbu set in it's neutral position the light bulb lite up as soon as I connected the power wire. Turn the switch with a screwdriver and the light goes off then comes back on as you continue to turn it. NSBU from Rockauto didn't lite up until it was turned a couple of clicks. Would this be an acceptable way to test the switch to see if it's good?
Attachments
Yes. Could cause the clocking of the switch to be off.
My GM service manual documents a cable adjustment procedure, but i found this writeup elsewhere on the web, which is pretty much what the manual says.
The shift cable comes in two pieces and where they meet there's a slack adjuster. It's on the drivers side of the truck right below the door on the outside of the frame rail. Here are the adjustment instructions:
1. Place the steering column shift lever back into the park (P) position.
2. Raise the vehicle.
3. Ensure that the transmission manual shaft lever is in the park (P) position.
4. Pull the white cover back to expose the natural colored lock. Under the lock, insert a flat bladed screwdriver under the lock ramp located at the top of the lock. The lock will pop up, and the transmission end will move slightly away from the shifter end.
5. Push the end of the transmission end inside the shifter end until the blue spring on the transmission end is fully compressed, this will engage the inner wire and lock both wires together.
Important: DO NOT hold the transmission end during this operation, this will result in a mis-adjusted cable.
6. Release the transmission end and allow the spring to tension/adjust the cable system.
7. Pull the white cover on the shifter end back.
8. Push the natural colored lock button down to engage the locking teeth on the transmission end.
9. Release the white cover.
10. Verify the white cover conceals the natural colored lock.
Yup. The light should come on in P and N positions only, between C2-E and C2-G.
A word of warning: that light bulb could be drawing significantly higher current than what the wiper contacts inside the NSBU are rated for. Normally current passes through these for a relay coil which is normally < 0.5amp. Would advise using a smaller / lower current bulb like an automotive test probe lamp to avoid burning your NSBU contacts. $3 at Harbor Freight.
If you wanted, you could also repeat the test with the C2-C and C2-F pins, which would cause the light to come on in R position.
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this is good advice. that bulb is probably drawing 4 or more amps. that's probably about double what the contacts can handle short term
It ended up being a bad 7 pin connector. Replaced it and the truck fired right up. I'm down to 24 transmission codes now and the truck still won't engage in any gear. I pulled the circle plug from the back of the transmission and it had transmission fluid in, cleaned it out with electrical contact cleaner and compressed air and no change in codes. I ordered a new pass through connector seal that will be here Thursday.
Since you said the 7 pin and 4 pin NSBU connectors were new Rockauto items, perhaps the 4 pin is also bad, leading to your codes? For sure fix the pass through connector seal first.
Thanks for reporting back, this may help others in the future.
I replaced the 4 pin connector as well and installed the new pass through seal. Truck will engage in R and move but will not move in D. When you shift it into D the range shift inhibited message comes up on the dash. I have 19 TCM codes, I attached a picture of them. I tested pin C on the circle plug at the Allison and I have 12v. I tested pin G on the circle connector and I have 5v (P0711 TFT sensor circuit). Would the next step be pulling the pan off of the transmission and inspecting the internal harness? Not 100% sure what direction to go in next.
